July 12, 2016
By Tom Shelton, D.V.M.
Coronavirus has long been identified as a leading cause of calf scours and winter dysentery in adult cows. This is the second article of a two-part series that looks at the possible role of bovine coronavirus in bovine respiratory disease.
In the previous post, we discussed recent improvements in diagnostic testing that have identified bovine coronavirus (BCoV) as a possible agent in the cause of bovine respiratory disease (BRD). This post looks at results of a 2010 BRD study conducted by the Wisconsin Veterinary Diagnostic Laboratory (WVDL) in collaboration with Merck Animal Health.
Veterinarians in the major dairy-producing states were instructed to sample Holstein dairy calves younger than 6 months of age with BRD that had been sick for fewer than five days and had not been treated with antibiotics or received a BRD vaccine within 21 days of becoming ill. Five to six calves were sampled from each premises that was experiencing respiratory disease.
One hundred and ninety Holstein dairy calves from 32 different premises and 12 different states had pharyngeal swabs collected and sent to the WVDL for testing. There was no difference in the prevalence of respiratory disease pathogens found between the four different regions of the country and there was no difference in the median age of the calves (7.8 weeks) when they were first affected with respiratory disease.
Researchers found that BCoV, BRSV, Mycoplasma bovis and Pasteurella multocida either alone or in combination accounted for greater than 90 percent of the respiratory pathogens in the calves used in this study. Calves that were real time PCR positive for BCoV were more likely to also be pharyngeal swab positive for Mycoplasma bovis (p < 0.05).
Results (Table 1) show no statistical difference in the prevalence of BHV-1 and BVDV, but there was a statically higher prevalence of BRSV and BCoV when compared to BHV-1 and BVDV (p < 0.05). The prevalence of BCoV was statistically higher than the prevalence of BRSV (p < 0.05).
Table 2 provides results for respiratory bacteria. There was no statistical difference between the prevalence of Mycoplasma bovis and Pasteurella multocida but they were both found at a higher prevalence (p < 0.05) than the other respiratory bacteria.
“While the importance of coronavirus as a primary pathogen in BRD is open for debate, this research clearly shows that coronavirus is very common in U.S. dairy calf operations,” says Donald Sockett, D.V.M., M.S., Ph.D., Diplomate ACVIM, epidemiologist/microbiologist, University of Wisconsin-Madison, Veterinary Diagnostic Laboratory.
|No. Coronavirus Positive||No. BRSV Positive||No. BVD Positive||No. BHV-1 Positive|
|32||25 (78.1%)||11 (34.4%)||2 (0.06%)||1 (0.03%)|
|99 (52.1%)||24 (12.6%)
|2 (0.01%)||1 (0.005%)|
|No. Mycoplasma bovis Positive||No. Pasteurella multocida Positive||No. Histophilus somni Positive||No. Mannheimia haemolytica Positive|
|32||28 (87.5%)||29 (90.6%)||5 (15.6%)||13 (40.6%)|
|101 (53.2%)||86 (45.3%)||9 (4.7%)||22 (11.6%)|
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